The present invention generally relates to display of a color image with use of color look up tables (which will be referred to merely as the CLUTs, hereinafter) and, more particularly, to a color image displaying method for switching a plurality of images to be displayed.
In a color image displaying method in digital processing, the luminance levels of each of three primitive colors of R (red), G (green) and B (blue) are expressed in terms of 2.sup.3n of n-bit color data. In such a method that one color data is held for each pixel in a display image for color display, a display memory is required to have a capacity of 3n bits per pixel.
Meanwhile, in a color display method using a CLUT, a data per pixel is expressed in terms of an m-bit color code and the color code is converted into the luminance levels of the R, G and B to express 2.sup.m of colors. In this display method, since a display image is formed through the CLUT and a bit map made up of the color codes associated with the pixels and the amount of data in the bit map is proportional to m, the amount of necessary image data can be reduced. Further, by modifying the CLUT for converting the color codes into the luminance levels of the R, G and B, the display color can be easily modified even with use of the same bit map data.
There has been proposed a method for simultaneously displaying a plurality of images with a limited number of displayable colors, wherein color code data are divided into a plurality of blocks, one image is allocated to each block, and CLUTs are operated on every block basis to realize the simultaneous display of the plurality of images.
An example of such display method is disclosed in Japanese Patent Application Hei 3-61995.
In the prior art display method, the color code data are divided into a plurality of blocks with respect to its depth direction, one image is allocated to each block, and the CLUTs are switched to display the image seemingly differently with respect to part of the bit map regions.
However, since the plurality of images are displayed as overlapped with each other, one of CLUT numbers of each of the CLUTs for the images must has a transparent color.
Further, since the plurality of images are displayed as always overlapped with each other, the method has a problem that such image effects as fade-in, fade-out, cross fade and glowing cannot be obtained.
Furthermore, since the bit maps are composed on a display memory, this disadvantageously requires a special display circuit.